This invention relates generally to textile thread cutters, and more particularly to such cutters that utilize a vacuum source and that are employed as part of a continuous sewing operation immediately after stitching by a sewing machine.
Vacuum thread cutters are generally well known, as exemplified by U.S. Pat. Nos. 2,356,378 (Capolupo (1943); 2,607,101 -- Stout (1952); and 3,557,730 -- Armstead (1971). In this type of mechanism, a vacuum system is used to pull trailing chain stitch threads through a cutting element as the sewn cloth leaves a sewing machine. The vacuum both holds the thread in position for the cutters and removes the cut thread from the work station.
A problem common to most of such prior art trimmers when used with an automated sewing machine operation is that because the workpiece is removed automatically at a relatively rapid rate, the trailing chain stitch is drawn taut and passes over the cutting shears without being severed. The result is that the workpiece is still tethered to the sewing machine and is pulled free to the workpiece removal mechanism, thereby upsetting the sequence of operations of the entire automated system. One way to overcome this problem is to ensure that during removal of the workpiece from the sewing machine, slack is allowed to occur in the chain stitch. The slack in the chain stitch can then be sucked by a vacuum line into engagement with the cutting shears. This, however, necessitates that there be a pause in the removal operation which slows the severing operation.
It is a principal object of the present invention to provide an improved vacuum head thread cutter that positively severs a sewn workpiece from the sewing needle without the necessity of slowing the removal of the sewn workpiece from the sewing machine.
It is another object of the present invention to provide such an improved vacuum thread cutter that operates at increased rates of speed of cloth travel over the cutting station.